Impregnated leather and means of producing



2,983,566 IMPREGNATED LEATHER AND MEANS OF PRODUCING Seymour S. Klemen and Robert Lee Southwood, Cin-' cinnati, Ohio, assignors to Leather Research Corporation, New York, N.Y., a corporation of Delaware No Drawing. Filed Apn ls, 1958, Ser. No; 729,233

' 16 Claims. (Cl. 8-94.21)

This invention relates to the preparation of improved leathers such as sole leathers, and aims to provide new impregnated thicker leathers, which are characterized by having desirable properties derived from the impregnants without the undesirable properties hitherto obtained when leather is impregnated. Theinvention is also directed at novel methods for impregnating hide material which produce the desirable new leathers. In its most preferred aspect, this invention is directed to the production of tanned thicker leathers with unique properties, from hide material which has been dehydrated by replacement of the water therein with water-miscible readily volatile organicliquids such as the lower alkyl ketones and alcohols.

Conventionally, sole leather is prepared from full cattle hides (comprising about 23% hide collagen in the'salt cured state) by a vegetable tanning. process. The salt cured hides, as received by the tannery from the meat packers, are soakedto removesalt, bloodetc." They are then lime treated to lo'osenthe hair, which is next removed. A treatment with deliming salt and enzyme, known as bating, prepares the hides for tanning. At this stage of the process, the hides will contain about 25% by weight ofhide collagen; the balance is principally water. The hides are then exposed to the tanning procedure, by being put into progressively stronger solutions of vegetable tanning agents such as quebracho, chestnut, oakgall etc. Since the tanning agent combines as it penetrates, and this tanning effect retards further penetration, completetanning requires several weeks in common commercial practice, and to achieve penetration considerably more tanning agent must be picked up than the minimum necessary to chemically stabilize the collagen. It is estimated that as little as 4 to 6 poundstannin would tan the 23 pounds of collagen present in 100 pounds of cured hides if properly distributed-4 Actually, about 30 pounds of tanning agent is present in the finished leather made from this 23 pounds of collagen. Most ofthis quantity of tanning agent is required to ensure complete penetration of tanning agent through the leather.

It was proposed as early as 1910 toshorten; the tanning process by using. the so-called solvent tanning method. In this method, the wet bated hides are treated with a low-boiling water-miscible solvent like methanol, ethanol, isopropanol or acetoneywhen the water has been removed by the solvent, the solvent is dried off to give a dehydrated hide which is essentially porous hide substance. Solvent dehydrationis used to prevent-the closing up of the pores whichoccurs whenthe water is redifiicult to obtain on large pieces. Finally, it has been difficult even in laboratory operations to keep the leather sufficiently plump during finishing, sothat the finishedleather lacks body. The problems of economical dehydration and uniform tannage have been overcome, using the processes described in our copending application, Serial No. 535,755, filed September 21, 1955, now US. Patent No. 2,917,833. However, attempts to get plumpn'ess and body by the use of impregnants such as resin have produced material ofpoor quality, which finish poorly and have cracky grains.

It is an object of the present invention to impregnate previously prepared leather with resin in such fashion that the finishing qualities of the previously prepared leather are not impaired, and to impregnate solvent dehydrated hides with resinso that the finishing operations are substantially reduced as compared with ordinary leather.

It is a further object of this invention to produce leathers which have desirable plumpness, are lighter, in

weight than conventional leather, as wellas to produce leathers which are more waterproof than conventional leather, and possess added abrasion resistance, controlled firmness and good cutting properties.

In accordance with the present invention, porous hide,

material, either before or after tanning, is impregnated Witha solution of a non-tanning impregnant; the impregnated hide material is then rinsed with a solvent'for the impregnant to reduce the concentration of the impregnant in the outer layers of the hidematerial; and the impregnant solvent is then extracted with a material which dissolves the impregnant solvent but not the impregnant, so that the impregnant'isprecipitated in the hide material in substantially greater concentration at the center of the material than at the ouer layers. The hide maerial is preferably tanned before orduring the process, so that an impregnated leather results directly, or it may be tanned after setting the impregnant.

The resultant product is an impregnated leather which hasthe desirable characteristics imparted to it by thecentral layer of impregnant, but has the excellent finishing characteristics of non-impregnated leather, due to the relative freedom from impregnant of the surface layers.

The process and product of this invention differ markedly from prior art impregnated leather impregnation a material before or after tanning, in a solution of imtion, after rinsing excess impregnant from thefsurface pregnant in a volatile solvent, and heatingthe hide material to drive oif the solvent. Wehave found that this procedure causes a migration of the impregnant to the surface layers and producesleatherswithless impregnant in the interior than at the surfaces. Rinsing of the sur face prior to evaporation is'of little help in solving the problem; migration and excessive impregnant. concentration at the surface still result. It is only when the impregnant is precipitated in accordance with this invenlayers, that the desirable results of the instant invention i s are obtained.

depositing the tanning agent throughout the, hides. If the In carrying out the "invention with ordinary tanned leathers'in the unfinished state, improved abrasion resistance, firmness and resistance to water uptake can be obtained with materials such as resins, waxes, oils, plas ticizers, cellulose derivatives'and elastorriers 'shch asnat After treatrnentythe leath ural and synthetic "rubbers. ers are finished in conventional fashion;

Even better results are obtainable with untanned hide which may be used is described andclaimed in thecopending Kremen et al. application Serial No. 535,755,: filed September-2.1, 1955. Such dried hides maybe im-" v 3 mcrsed in solutions, preferably in acetone or a lower alcohol, containing both an impregnant, such as described in the preceding paragraph, and a tanning agent.

In the next step, the hides are rinsed, preferably by immersion, with a solvent for the impregnant, preferably the same solvent used for impregnation, either with no impregnant or a low concentration of impregnant. In ordinary plant operations, the rinsing solvent will build up to a relatively low impregnant content rapidly, and then will stay at that figure. The maximum impregnant content permissible in the rinse is a fraction of the amount permissible in the outer layers of the finished leather. In general, amounts as high as 20% have little or no effect; higher amounts can be tolerated with many impregnants.

In the third step in the process, the hides are again treated, preferably by immersion, with an extracting solvent which dissolves the impregnant solvent but precipitates the impregnant. This extracting solvent is prefeerably water, which removes the solvent, acts to set the tanningagent and precipitates the impregnant.

Since the impregnant will not migrate in the presence of a non-solvent, the extraction solvent may be removed by evaporation, or may itself be extracted with a volatile extraction solvent which is a non'solvent for the impregmant preferably'by water to complete the tanning.

The resultant leather now has aconcentration of impregnant in the interior, and outer grain and flesh surfaces relatively free of impregnant, and with substantially less tanning agent than in conventional leather. As. a result, finishing operations are substantially eased, :and improvedfinish can be obtained with less efiort, the body, firmness, plumpness and strength being provided by the impregnants in the body of the leather.

Typically, a standard tanned sole leather will contain, per 100 pounds of hide substances, about 120 pounds of tannin and 60 to 80 pounds of finishing material; the resultant leather will have a specific gravity of about 1.0 or more. When the instant process is used with solvent dehydrated hides, the same 100 pounds of hide substance will contain less than half as much tannin as hide substance, preferably about one-third as much, and from 10 to 60 pounds of impregnant, plus less finishing material than standard leather. By proper choice of impregnants, it can have approximately the same volume as standard leather, and yet have a specific gravity as low as 0.65. I

The invention cannot beapplied to the production very thin leathers, because the rinsing operation removes material down to a depth of about 4 inch (called an iron in the leather trade), Hence, in a. piece only inch in thickness, a rinse will remove substantially all of the impregnant. For the invention to have practical utility, the unrinsed layer should be at least almost equal to the rinsed layer in thickness; hence, the invention requires that the hide substance being treated have a thickness of about 35 inch (3 irons).

The following typical examples of the invention are supplied by way of example and not as a limitation on the invention, which can be practiced with a wide variety of other materials, and in other manners, as defined in the claims.

' Example I.-Pretanne'tl leathers Three samples of leather were selected. One was a i still porous.

A solution was prepared consisting of:

I p I Pounds Dymerex resin (dimerized'rosin) 20 Parafiin wax (M.P. 50 C.) ..10

99% isopropanol, 120 F.

- i Y Parts byweight Raw quebracho (20% water-% solidsabout 65% tannin) 5 Dymerex resin (dimerized rosin) 20 Parafiin wax (M.P. 50 C.) l0, 7 Formaldehyde'(added as 40% formalin) 2 Water (from the formalin) 3 Acetone u 60 The leathers were immersed in the solution, at F., for'20 minutes. The pieces were drained, and then immersed for 10 minutes in a solution consisting of:

. Parts by weight Above resin wax solution 1 99% isopropanol at 120 F. 4

When Vinsol resin (paratfin hydrocarbon insoluble resi-' due obtained in the purification of wood rosin) was used, properties were identical, except that the leader had a definite yellowish color.

Example II.Pretanned leathers with non-aque0us precipization The three leathers of Example I were again used, andimme-rsed for 15 minutes in a solution consisting of:

, Pounds Polybutene (medium mol weight) 20 Methylene chloride 80 at room temperature.

In one group of tests, the three impregnated leathers were rinsed by a 15. minute immersion in a 4% solution of polybutene in methylene chloride; in'a second group of tests, the leathers were rinsed by a 10 minute immersion in pure methylene chloride. Results were comparable.

The methylene chloride was removed by immersion of the samples in acetone for two hours. One of the samples was treated with isopropanol, with similar results. The samples were removed from the extracting solvents, drained and the acetone or isopropanol removed by evaporation.

The resultant leathers were equally satisfactory during finishing, and had the same appearance as the original leathers. The leathers exhibited improved flexibility, water resistance and abrasion resistance.

Example III.--Impregnafi0n with butyl rubber leather was essentially similar to that obtained in Example II from the same leather.

Example I V.Untanned hide substance An unsplit cow hide was dehydrated by extraction with acetone, and the acetone evaporated off under conditions that prevented wrinkling of thehide as described in application Serial No. 535,755 filed September 21, 1955. It"

was immersed in a solution comprising:

at 120 F., and allowed to stayfor 15 minutes to ensure I completeimpregnation. a

- The hide was drained and immersed in a solution at 120 F.','comprising:.

. resin).

Epon 1001. (bisphepol epichlohydrin Dymerex Parts by weight Quebracho extract as above 5 Dymerex resin 4 P-arafiin wax as above 2 40% formalin 1 5 Acetone 88 After minutes, the hide was withdrawn, and immersed in water for several hours, and dried. The resultant tanned leather was about 9 to 10 irons 0 thick, had a high abrasion resistance, low water uptake, very low specific gravity (0.65), excellent chemical and thermal stability, resistance to perspiration, and a very natural appearing surface which responded so readily to finishing operations that a desirable finish was obtained with far less labor and material than for conventional quebracho tanned leather.

In this case, the quebracho extract, which does part of the tanning, was purposely kept at the same level on the surface as on the interior. The formaldehyde which imparts resistance to compacting during the finishing operation, was reduced by rinsing to assure against crackiness in the grain. This special utility of formaldehyde is described and claimed in the copending Kremen and Southwood application Serial No. 729,254, filed April 18, 1958.

Example V Example IV was repeated, except that the 5 parts of formalin in the impregnation solution was replaced by 5 parts of quebracho extract, and the formalin in the rinse solution was replaced by acetone. The resultant leather was slightly less firm than the leather of Example IV, but otherwise had similar properties.

hide similar to that used in Example IV. Ineach case, the formula used was as follows:

Parts by weight Resin 20 Formcel (55% formaldehyde-% methanol) -s--- 5 Acetone 75 Ineach case, the dehydrated hide was immersed in the solution of resin. and then rinsed in a rinse comprising 1 arts by weight Originalsolution -4. 20 Acetone 80 After rinsing, the solvent was extracted with water containing 1% formaldehyde, and the piece dried. Resin uptake varied from 20% to 30%, except as indicated below; the formaldehyde tanned leathers resulting were allwater-resistant and firm. Comments show differences from the sample made from Dymerex resin.

Uptake, Comments Percent Resin Very paleicolor.

Leather softer than Dym erex.

Good color.

Resin only partly soluble; Results uncertain.

Orangeshellac Heavy color.

Polyvinyliormal 2 Excellent color.

95 second cellulose butyrate. G ood color.

Polyispbntyl methacrylate 24 Do.

Becltamine P196 (urea iormalde Do.

condensation product). OnmanResinC (coumaroneresinhpn r Piccolyte 450$ (coumarone indene.

resin). Vinsol Firm;

Dirty color.

Polypale (polymerized rosin) i The example indicates that in general, resins can be used as a general class as well as elastomers, to impregnate hide substance by the process of the invention.

Example VII A hide similar to that used in Example IV was split to produce a grain split about 4 /2 irons thick. It was immersed for 10 minutes in a solution at 120 C., con

The impregnated split hide was drained, and rinsed with a solution of Quebracho extract 1.6 Dymerex resin 1.6 Paraflin wax 1.0 Paraffin oil 0.6 Distilled animal fatty acids as above 0.6 Methyl formcel 1.0 Acetone 93.6

by immersion for 10 minutes. at 120 F. The rinsed split hide was drained, immersed in water for an hour, drained and dried. It was finished in the conventional manner used for upper leathers, and gave a satisfactory finished upper with less than normal labor. The. leather had better water resistance than conventional upper leathers.

Example VIII Example IV was repeated, except that the impregnating solution consisted of:

Parts by weight Dymerex resin 20 Parafiin wax (Melting point 50' C.) 10 Methyl formcel (55% formaldehyde-45% methanol) v 5 Distilled fatty acids (oleic-stearic acid mixture) 2.5 Acetone 62.5

and the rinse solution consisted of 20% of this impregnating solution, acetone. Afterthewater immersion, however, the wet hide was immersed for one hour in lukewarm water containing 10% of a powdered oisulfite-quebracho extract, at pH 3 to 4; After thisimmersion, the hide was drained and'dried. The resultant leather had:a surface color and character about identical with conventional quebracho tanned sole leather. However, it was much more water resistant than either conventional leather. or the leather of Example IV, since thehydrophilic quebracho was present only in the surface layers of the leathers. As a result, only the surface was wettable, an ideal situation, since the surface must be Wettable for rolling in the finishing operation, whereas a hydrophobic water-impervious interior makes the leather proof to penetration by water.

' Tan liquors other than the specific quebracho extract shown can be used to give the desired surface appearance and finishing characteristics.

Example IX r A series. of soleleathers was prepared from. an'unsplit cow hide like that described in Example IV, with three different impregnating solutions, as follows:

In each case, the dehydrated hide was immersed in the impregnant for 15 minutes at 120 F., drained and immersed in the original bath diluted with four times its weight of acetone, for 10 minutes at 120 F., drained, immersed in water for several hours and dried.

All the leathers finished more readily, and gave lighter, more water-resistant leathers than conventional quebracho tanned leather; abrasion resistance was likewise improved.

Leather A had the desired stifiness desired by cobblers in finders leather; leather B had the feel and stiffness appropriate for mens shoe manufacture; and leather C was softer, and met the requirements for ladies shoe soles.

These leathers may be advantageously treated with a vegetable tan after water immersion, before drying, as in Example VHI.

' Example X An unsplit cow hide, dehydrated by extraction with acetone, was impregnated with a solution containing:

Parts by Weight "Quebracho extract as in Example IV 15 Vinsol resin 16 Paraffin wax, M.P. 50 C. l'Distilled animal fatty acids as in Example VII 3 Acetone 61 'The dehydrated hide was immersed in the impregnant for fifteen minutes at 120 F., drained and immersed in a solution of 15 parts by weight quebracho extract and 85 parts by weight of acetone for ten minutes at 120 F., drained, innnersed in water for several hours and dried.

This leather contained about 30% of tannin, based 'on hide substance. It is somewhat darker in color than standard sole leather, more water resistant, much lighter in weight. As compared with the leathers of Example IX, it compacts slightly more.

Obviously, the above examples can be multiplied indefinitely. The process opens up to the leather manu facturer the use of any impregnant which is soluble in any solvent, since the solvents can in turn be extracted .with agents which will precipitate the impregnant while removing the solvent therefor. Obviously, the solvents used should be inexpensive and preferably of low boiling point, so that they can be economically recovered. And most advantageously water-insoluble impregnants dissolved in water-miscible solvents are the most economic materials to use in the process, since this reduces the solvent recovery problem to a single solvent, and permits tanning to take place during the solvent removal impregnant precipitation step.

Typical of the impregnants which may be used are the natural and synthetic resins, cellulose derivatives, soluble waxes and natural and synthetic rubbers in soluble form; unpolymerized or partially polymerized materials which can be converted in the leather before the drying operations so as not to migrate, may also obviously be used. The properties of these impregnants may be modified in known manner by adding plasticizing agents, stabilizers, lubricating agents such as waxes and the like, to improve stability,-waterproofness, flexibility and.workability of the finished leather.

While the invention has been described as applicable to the preparation of leather from cattle hides, it may obviously be applied tothe preparation of leather gen- 8 erally where the skins are at least about $4 inch in thickness.

What is claimed is:

1. Leather characterized by the fact that it contains water insoluble impregnants other than hide substance and tanning agents therefor, the impregnants being substantially less concentrated in the surface layers than at the center.

2. Leather about 1 inch or more in thickness and containing water insoluble impregnants other than hide substance and tanning agents therefor, the impregnants being substantially less concentrated in the surface layers of the leather than at the center thereof.

3. Leather of a thickness of at least inch containing a water insoluble non-tanning resinous impregnant, the impregnant being substantially less concentrated in the surface layers than at the center.

4. A leather tanned with vegetable tannins and containing in addition a water insoluble non-tanning impregnant, the leather being characterized by containing less than half as much vegetable tannin as hide substance,

and a lower concentration of non-tanning impregnant in the surface layers than at the center.

5. A leather tanned with vegetable tannins and formaldehyde, and containing in addition a water insoluble non-tanning impregnant, the leather being characterized by containing less than half as much vegetable tannin as hide substance, and a lower concentration of nontanning impregnant and formaldehyde in the surface layers than at the center.

6. A leather tanned with vegetable tannins and formaldehyde, and containing in addition a water insoluble nontanning resinous impregnant, the leather being characterized by containing less than .half as much vegetable tannin as hide substance, and a lower concentration of non-tanning impregnant and. formaldehyde in the surface layers than at the center.

7. Themethod of producing impregnated hide substance which comprises impregnating porous hidesubstance with a solution of a water insoluble impregnant which is not a tanning agent for the hide substance, rinsing the wet hide substance with a solvent for the impregnant which contains no more than a small amount of said impregnant to reduce the concentration of impregnant in the outer layers of the hide substance, precipitating the impregnant in the hide substance by treatment with an extraction medium which is a solvent for the impregnating solvent and a non-solvent for the impregnant, and then removing the extraction medium to leave the impregnant in the hide substance in greater concentration in the center than in the outer layers.

8. The method of producing impregnated hide sub-- stance which comprises impregnating porous hide sub: stance with a solution of a water insoluble non-tanning resinous impregnant in a solvent therefor, rinsing the wet hide substance with a solvent for the impregnant which contains no more than a small amount of said impreg-' nant to reduce the concentration of impregnant in the outer layers of the hide substance, precipitating the impregnant in the hide substance by treatment with an extraction medium which is a solvent for the impregnating. solvent and a non-solvent for the impregnant, and then removing the extraction medium to leave the impregnant in the hide substance in greater concentration in the centreatment with an extraction medium which is a solvent for the impregnating solvent and anon-solvent for the impregnant, and then removing the extraction medium to leave the impregnant in the leather in greater concentration in the center than in the outer layers.

10. The method of producing impregnated leather from dried porous untanned hide substance which comprises impregnating the hide substance with a solution of a water insoluble non-tanning resinous impregnant and a tanning agent in a non-aqueous solvent therefor, rinsing the wet hide substance with a non-aqueous solvent for the resinous impregnant which contains no more than a small amount of said impregnant to reduce the concentration of the impregnant in the outer layers of the hide substance, precipitating the impregnant in the hide substance by treatment with an extraction medium which is a solvent for the impregnant solvent and a non-solvent for the impregnant and then removing the extraction medium to leave the impregnant in the hide substance in greater concentration in the center than in the outer layers.

11. The method of producing impregnated leather which comprises impregnating a dried porous hide substance with a solution of a water insoluble non-tanning resinous impregnant and a tanning agent in a nonaqueous solvent therefor, rinsing the wet hide substance with a water-miscible solvent for the impregnant which contains no more than a small amount of said impregnant to reduce the concentration of impregnant in the outer layers of the hide substance, treating the hide substance vvith water to precipitate the impregnant, set the tanning agent and remove the solvent from the hide substance, and then removing the water to leave the impregnant in the hide substance in greater concentration in the center than in the outer layers.

12. The method of claim 11, in which the non-aqeous solvent and the water-miscible solvent for said impregnant each comprise the same solubilizing substance.

13. The method of producing sole leather which comprises impregnating a dried porous untanned cow hide with a solution containing vegetable tannin, water insoluble resin and formaldehyde in a water miscible organic solvent for the vegetable tannin, resin and formaldehyde, rinsing the wet hide substance with a water miscible organic solvent which contains no more than a small amount of resin and formaledehyde to reduce their concentration in the outer layers of the hide, precipitating the resin, and simultaneously removing the organic solvent and causing the tannin and formaldehyde to react with the hide to produce a tanned leather, by treatment with water, and then removing the water leaving a tanned leather in which the resin and formaldehyde are in greater concentration in the center of the leather than in the outer layers.

14. The method of claim 13, in which the organic solvent is acetone.

15. A sole leather having a specific gravity of substan-' tially under 1.0, the interior fibers of which are impregnated with sufficient resinous impregnation to render the 10 leather water resistant and which are tanned with sufliganic solvent for the resinous impregnant and the formaldehyde which contains no more than a small amount of the resinous impregnant and the formaldehyde to reduce the concentration of the resinous impregnant and the formaldehyde in the outer layers of the porous hide substance, treating the hide substance with water to precipitate'the resinous impregnant, set the formaldehyde and remove the impregnant solvent from the porous hide substance to produce a leather having substantially more resinous impregnant and formaldehyde combined with hide substance in the interior of the leather than in the outer layers thereof.

References Cited in the file of this patent UNITED STATES PATENTS 2,582,298 Ushakotf Ian. 15, 1952 2,766,134 Davis Oct. 9, 1956 2,824,816 SOmerville et al. Feb. 25, 1958 FOREIGN PATENTS 565,065 Great Britain Oct. 25, 1944 OTHER REFERENCES Davis et al.: Journal of the American Leather Chemists Association," January 1955, 1, pp, 38-42.

Progress in Leather Science, 1920-1945, British Leather Manufacture Research Assoc, London, 1948, pp. 666 and 667. 

7. THE METHOD OF PRODUCING IMPREGNATED HIDE SUBSTANCE WHICH COMPRISES IMPREGNATING POROUS HIDE SUBSTANCE WITH A SOLUTION OF A WATER INSOLUBLE IMPREGNANT WHICH IS NOT A TANNING AGENT FOR THE HIDE SUBSTANCE, RINSING THE WET HIDE SUBSTANCE WITH A SOLVENT FOR THE IMPREGNANT WHICH CONTAINS NO MORE THAN A SMALL AMOUNT OF SAID IMPREGNANT TO REDUCE THE CONCENTRATION OF IMPREGNANT IN THE OUTER LAYERS OF THE HIDE SUBSTANCE, PRECIPITATING THE IMPREGNANT IN THE HIDE SUBSTANCE BY TREATMENT WITH AN EXTRACTION MEDIUM WHICH IS A SOLVENT FOR THE IMPREGNATING SOLVENT AND A NON-SOLVENT FOR THE IMPREGNANT, AND THEN REMOVING THE EXTRACTION MEDIUM TO LEAVE THE IMPREGNANT IN THE HIDE SUBSTANCE IN GREATER CONCENTRATION IN THE CENTER THAN IN THE OUTER LAYERS. 